Cliffs Natural Resources Inc. is selling its Renewafuel operations near Marquette and returning its $500,000 Community Development Block Grant to Marquette County. The plant has been up and running, producing high-energy, low emission biofuel cubes from wood and agricultural feed stocks designed to help meet renewable portfolio standards and/or air emission limits. Before shutting down, the plant delivered its first supply of biofuel cubes in July to the Marquette Board of Light and Power as a coal substitute.